Exploring the relationships between gully erosion and hydrology in rangelands of SW Spain
Gómez-Gutiérrez, Álvaro; Schnabel, Susanne; De Sanjosé, José Juan; Contador, Francisco Lavado
published: Jan 1, 2012
ArtNo. ESP023105601004, Price: 29.00 €
Gully erosion plays an important role in degradation processes of Mediterranean environments. In SW Spain, gullies are frequently located on valley bottoms where they erode shallow alluvial deposits. This study was carried out on a small discontinuous gully in a wooded rangeland catchment (99.5 ha). The objectives of this work were: (i) to quantify the soil losses by gully erosion processes in a small catchment representative of dehesa (rangeland) land use, (ii) to analyze the spatial and temporal variability of gully erosion and (iii) to identify the processes acting in the channel and (iv) to analyze the relationships between gully erosion and catchment hydrology. Gully monitoring was carried out by measuring the evolution of the gully cross sections at 28 fixed locations using a laser total station and with a frequency of 6 months during the period 2001-2007. Discharge and rainfall were registered automatically by means of a compound weir at the outlet of the catchment and 6 rain gauges. Results showed an erosion of -4.17 m3y-1. The records presented a high temporal variability, with larger sediment losses observed during the first semester of the hydrological year, while net accumulation was dominant during the second part of the hydrological year. Significant relationships were obtained between the amount of total net erosion-accumulation and hydrological variables, such as total discharge and the number of times peak discharges exceeded certain values. However, the closest relationship was observed with the total rainfall amount of the period (R2 = 0.90). We argue that besides the characteristics of the channel flow, an important factor of gully growth is the water content of the valley bottom sediments. Large amounts of rainfall produce water saturation of the sediments and reduce the cohesion of the channel banks, thereby enhancing its erodibility. Channel aggradation was probably related with the input of sediments originating from sheetwash along the hillslopes during periods with low rainfall amounts.